There are around 700 people who work in the firm's Perth office, which will face closure. Bases in Edinburgh, Cumbernauld and Dunfermline also set to close.
Unite said it aimed to secure "as many jobs as possible”.
However, staff have been told that 1,700 employees across the UK will lose their jobs through voluntary redundancy.
Offices in Glasgow, Bristol and London will continue to operate and more employees will be supported to work from home following the closures, the provider has said.
Elaine Dougall from Unite told BBC Radio's Good Morning Scotland programme the talks would give a better idea of how many jobs were affected in Scotland.
She said: "Once jobs go from the market it's almost impossible to get those jobs back.
"So from a Scottish perspective we want to try and save as many of those jobs as possible because that has not only an impact on the workers, but also in the wider communities.
"Those are good, high-quality, well-paid, pensionable jobs that those people have secured for a number of years and we want to try as much as possible to keep those jobs here in Scotland."
The cuts come after the provider recently reported losses to the business.
Asked if job cuts were inevitable, Ms Dougall said any "streamlining" should come "across the piece and not just hit frontline staff in the first instance".
The job cuts are understood to be linked to the company's acquisition of SSE's household energy business three years ago and the integration of the firm into Ovo.
The firm also said it would create a new "Ovo Academy" in Glasgow, creating "new opportunities in the city that hosted COP26 for those who want to be at the forefront of the UK's green revolution".
Ovo Energy, which was launched in 2009, claims it was launched to make “energy cheaper, greener and simpler”.
The gas and electricity provider is committed to being a net zero carbon business by 2030.
Confirmation of base closures comes as energy company E.ON was forced to apologise after sending socks as presents to customers as a way to help them keep warm ahead of a massive spike in energy prices.
The company shipped a free pair of polyester socks to 30,000 households it supplies with energy.
The customers had reportedly engaged with one of E.ON’s energy saving campaigns last year and the socks were there to encourage them to continue to save energy.
But E.ON said it should not have gone ahead with the plan in light of major price rises that are about to hit millions of households.
“If you recently received a pair of socks from us, we would like to say we are incredibly sorry for how we have made some people feel,” the company said.
“In light of the seriousness of current challenges that many people are facing, this mailing should have been stopped and we are sorry.”
The apology comes just days after rival firm Ovo said it was sorry for giving customers advice on cuddling up to pets to save energy.